A stent delivery system is disclosed in which a stent is contained in a sheath in an initial state and the stent is released inside a living body lumen in accordance with a movement of the sheath in a proximal direction with respect to an inner member. A movement mechanism of the stent delivery system has a rack member which is connected to a proximal end of the sheath, and a plurality of pinions which move the rack member in accordance with rotations thereof.